Consider the reaction sequence from P to Q shown below. The overall yield of the major product Q from P is 75%. What is the amount in grams of Q obtained from 9.3 mL of P? (Use density of  P = 1.00 g mL^–1, Molar mass of C = 12.0, H = 1.0, O = 16.0 and N = 14.0 g mol^–1) 

 

Molecular weight of 
aniline = M.wt. of C₆NH₇
= 72 + 7 + 14 = 93
density of P = 1 gm ml^–1
9.3 ml of P = 9.3 gm P

$=\frac{9.3}{9.3}=0.1\text{ mole }\mathrm{P}$

The mole ratio PhNH₂ : PhN₂⁺ :

= 1 : 1 : 1 

so the mole of Q formed will be 0.1 mole and extent of reaction is 100% but if it is 75% yield.
Then amount of Q = 0.1 $\times \frac{75}{100}=0.075\mathrm{mol}$

The molecular formula of Q = C₁₆H₁₂ON₂

so M.wt. of Q = 16 × 12 + 12 × 1 + 16 + 2 × 14
= 192 + 12 + 16 + 28
= 248 gm
so amount of Q = 248 × 0.075
= 18.6 gm